Enteric Indicator Bacteria Research Articles

Effect of ultrasonic and ozone pretreatment on the fate of enteric indicator bacteria and antibiotic resistance genes, and anaerobic digestion of dairy wastewater

In this study, the effect of ultrasound (US), ozone and US combined with ozone (US/ozone) pretreatments on the fate of enteric indicator bacteria and antibiotic resistance genes (ARGs), and anaerobic digestion (AD) of dairy wastewater was investigated. The pretreatment conditions included US power 200 W, ozone concentration 4.2 mg O3/L, and pretreatment time 0–30 min. The results showed that US/ozone pretreatment was effective in the inactivation of enteric indicator bacteria. Total coliforms and enterococci were reduced by 99% and 92% after 30 min US/ozone pretreatment. Pretreatments could not decrease ARGs in absolute concentration, but could decrease ARGs in relative abundance. In the subsequent AD process, methane production increased more than 10% with 20 min ozone or 20 min US/ozone pretreatments. Pretreatment-AD together obviously inhibited the enrichment of ARGs in relative abundance. This study provided a pretreatment way to enhance methane production and to prevent the enrichment of ARGs.

The impact of municipal sewage sludge stabilization processes on the abundance, field persistence, and transmission of antibiotic resistant bacteria and antibiotic resistance genes to vegetables at harvest

Biosolids were obtained from four Ontario municipalities that vary in how the sewage sludge is treated. These included a Class B biosolids that was anaerobically digested, a Class A biosolids that were heat treated and pelletized (Propell), and two Class A biosolids that were stabilized using either the N-Viro (N-Rich) or Lystek (LysteGro) processes. Viable enteric indicator or pathogenic bacteria in the biosolids were enumerated by plate count, gene targets associated with antibiotic resistance or horizontal gene transfer were detected by PCR, and a subset of these gene targets were quantified by qPCR. Following application at commercial rates to field plots, the persistence of enteric bacteria and gene targets in soil was followed during the growing season. Carrots, radishes and lettuce were sown into the amended and unamended control plots, and the diversity and abundance of gene targets they carried at harvest determined. All three Class A biosolids carried fewer and less abundant antibiotic resistance genes than did the Class B biosolids, in particular the very alkaline N-Viro product (N-Rich). Following application, some gene targets (e.g. int1, sul1, strA/B, aadA) that are typically associated with mobile gene cassettes remained detectable throughout the growing season, whereas others (e.g. ermB, ermF, blaOXA20) that are not associated with cassettes became undetectable within three weeks or less. At harvest a larger number of gene targets were detected on the carrots and radishes than in the lettuce. Overall, land application of Class A biosolids will entrain fewer viable bacteria and genes associated with antibiotic resistance into crop ground than will amendment with Class B biosolids.

Anaerobic co-digestion of pig manure and food waste; effects on digestate biosafety, dewaterability, and microbial community dynamics

This study assessed the effect of varying pig manure (PM)/food waste (FW) mixing ratio and hydraulic retention time (HRT) on methane yields, digestate dewaterability, enteric indicator bacteria and microbial communities during anaerobic co-digestion. Three 10 L digesters were operated at 39 °C, each with a PM/FW feedstock composition of 85%/15%, 63%/37% and 40%/60% (volatile solids basis). While the PM/FW ratio was different among reactors, the organic loading rate applied was equal, and increased stepwise with reducing HRT. The effects of three different HRTs were studied: 41, 29, and 21 days. Increasing the proportion of FW in the feedstock significantly increased methane yields, but had no significant effect on counts of enteric indicator bacteria in the digestate or specific resistance to filtration, suggesting that varying the PM/FW feedstock composition at the mixing ratios studied should not have major consequences for digestate disposal. Decreasing HRT significantly increased volumetric methane yields, increased digestate volatile solids concentrations and increased the proportion of particles >500 µm in the digestate, indicating that decreasing HRT to 21 days reduced methane conversion efficiency High throughput 16S rRNA sequencing data revealed that microbial communities were just slightly affected by changes in digester operating conditions. These results would provide information useful when optimizing the start-up and operation of biogas plants treating these substrates.

Inactivation of enteric indicator bacteria and system stability during dry co-digestion of food waste and pig manure

Provision of digestate with satisfactory biosafety is critical to land application of digestate and to the anaerobic digestion approach to treating manure and food waste (FW). No studies have been conducted on digestate biosafety in dry co-digestion systems. The aim of this study was to assess the inactivation efficiency and possible inactivation mechanism for three enteric indicator bacteria and the system stability during dry mesophilic anaerobic co-digestion of FW and pig manure (PM). The effects of two different inocula were examined at a rate of 50% based on volatile solids (VS): digestate taken from existing dry co-digestion digesters and dewatered anaerobic sludge from a local wastewater treatment plant. The FW/PM ratios of 50:50 and 75:25 on a VS basis were also assessed. The results showed that using digestate as the inoculum and a FW/PM ratio of 50:50 led to stable dry co-digestion, with the specific methane yield (SMY) of 252mL/gVSadded. Total volatile fatty acid (VFA) concentration was a significant inhibition factor for methane production during dry co-digestion (P<0.001). The data also showed that dry co-digestion of FW and PM effectively inactivated enteric indicator bacteria. E. coli and total coliforms counts decreased below the limit of detection (LOD, 102CFU/g) within 4–7days, with free VFA identified as a significant inactivation factor. Enterococci were more resistant but nonetheless the counts decreased below the LOD within 12days in the digestate inoculum systems and 26–31days in the sludge inoculum systems. The residence time was the most significant inactivation factor for enterococci, with the free VFA concentration playing a secondary role at high FW/PM ratio in the sludge inoculum system. In conclusion, digestate as inoculum and the FW/PM ratio of 50:50 were preferable operation conditions to realize system stability, methane production and enteric indicator bacteria inactivation.

Statistical modelling anaerobic digestion for process optimisation and bench‐marking: a case study of E. coli inactivation across all Thames Water conventional sewage sludge treatment sites

AbstractUntreated sewage sludge potentially contains a wide range of enteric pathogens that present a risk to human health. Mesophilic anaerobic digestion (MAD) is the most‐favoured process for sewage sludge treatment in the United Kingdom. It is a well‐established approach to sludge stabilisation, but the mechanisms responsible for pathogen removal are poorly understood. Operational data collected by Thames Water from conventional MAD sites were statistically scrutinised to examine the effects of primary and secondary digestion on the removal of the enteric indicator bacteria, Escherichia coli, by using the IBM SPSS statistical software package for ANOVA, post‐hoc and multiple regression analysis. The results showed that the process temperature conditions at the MAD plants were equivalent to or exceeded the minimum estimated by the analysis necessary to comply with the 2 log10 removal standard for E. coli. The results also showed that primary digestion conditions (specifically temperature) sublethally damaged E. coli and increased decay in secondary digestion and therefore over the whole digestion process.

An investigation into the removal of Salmonella and enteric indicator bacteria from the separated liquid fraction of raw or anaerobically digested pig manure using novel on-farm woodchip biofilters

The objective was to investigate the removal of Salmonella and enteric indicator bacteria from the liquid fraction of raw and anaerobically digested (AD) pig manure in woodchip biofilters over a 14week (98day) period. Antibiotic susceptible Salmonella Infantis was detected in one influent material (liquid fraction of raw manure) on two occasions but was not found in the effluent at any time point. Furthermore, mean coliform reductions of 56% were observed in the biofilters treating the liquid fraction of raw manure. However, a mean increase of 228% was found in those treating the liquid from AD manure, despite the fact that the microbial challenge to these biofilters was lower. In addition, relatively high coliform counts were still present in the effluent from both biofilter treatments, especially in the systems treating the liquid fraction of AD manure. However, findings for Escherichia coli and Enterococcus were more promising, with reductions observed for both treatments (10 and 18.5% for E. coli and 71 and 87% for Enterococcus). Moreover, E. coli and Enterococcus were at, or just above, the limit of detection in the final effluents. Overall, although, there are no microbial limits for discharge or washwaters, the woodchip filter effluent would appear safe for discharge to waterways or use on-farm as regards Salmonella, E. coli and Enterococcus but not coliform. In conclusion, woodchip biofilters offer potential as a low-cost sustainable novel treatment option for the removal of pathogens from the liquid fraction of pig manure.

REMOVAL OF PATHOGENIC AND INDICATOR MICROORGANISMS BY A CONSTRUCTED WETLAND RECEIVING UNTREATED DOMESTIC WASTEWATER

Wetlands containing floating, emergent and submergent aquatic plants, and other water-tolerant species have been found to economically provide a mechanism of enhancing the quality of domestic wastewater. The use of constructed wetlands for the removal of indicator bacteria (total and fecal coliforms), coliphages, protozoan parasites (Giardia and Cryptosporidium) and enteric viruses was investigated. A pilot scale constructed wetland consisting of two cells, one planted with bulrush and the other unplanted bare sand, were used to compare their efficiency in removing pathogens from raw sewage. Overall more than 90 percent of all microorganisms studied were removed by either of the two systems with a 1 to 2 day retention time. Removal of all mentioned microorganisms was greater from the surface flow in the unplanted cell than in the planted cell, except for Giardia and Cryptosporidium, although the differences were not statistically significant. Enteric viruses, coliphages and indicator bacteria were found to penetrate 2 m below the surface, although concentrations were reduced by greater than 99 percent in both cells. Less virus penetration into the sand occurred in the planted wetland versus the unplanted wetland. Water temperature was found to be the most important factor in the removal of enteric bacteria and viruses, while turbidity reduction was related to Giardia removal. These results demonstrate that significant reductions of pathogenic microorganisms can occur in constructed wetlands receiving untreated domestic wastewater with only a 1–2 day retention time.

Near on-line detection of enteric bacteria using lux recombinant bacteriophage

The potential for a revolution in microbial testing can be perceived with the near on-line detection of indicator microorganisms. By definition, these are microorganisms present in significant numbers within a food which, while not pathogenic, can be related through increasing count to the increased probability of pathogen contamination. We have used recombinant lux+ bacteriophage to detect enteric indicator bacteria without recovery or enrichment in 50 min, provided that they are present at levels greater than 10(4) g-1 or cm-2. After a 4-h enrichment, samples having enteric counts of 10 g-1 or cm-2 can be distinguished from background.

Near on-line detection of enteric bacteria usingluxrecombinant bacteriophage

Abstract The potential for a revolution in microbiol testing can be perceived with the near on-line detection of indicator microorganisms. By definition, these are microorganisms present in significant numbers within a food which, while not pathogenic, can be related through increasing count to the increased probability of pathogen contamination. We have used recombinant lux + bacteriophage to detect enteric indicator bacteria without recovery or enrichment in 50 min, provided that they are present at levels greater than 10 4 g −1 or cm −2 . After a 4-h enrichment, samples having enteric counts of 10 g −1 or cm −2 can be distinguished from background.

Coastal bathing water quality: the application of water quality standards to Welsh beaches

European recreational water quality standards are based largely upon the enumeration of enteric indicator bacteria in the nearshore zone. The sampling strategies specified in current standards are not designed to provide management information which can be used to formulate strategies for the control of risk to the recreator population. Furthermore, the chosen parameter of water quality, namely the Escherichia coli concentration, is increasingly questioned as a suitable enteric indicator species. Recently, Britain has demonstrated an increased willingness to implement the spirit as well as the letter of the EEC 1976/160 Bathing Waters Directive. Water authorities and environmental health officers will be faced with the task of interpreting the data generated by the existing beach water quality monitoring programmes. They will increasingly be asked questions regarding the epidemiological safety of bathing water by the general public and resort towns. Such questions cannot be answered properly with present levels of data. Present European and North American standards are applied to Welsh coastal bathing sites with the aim of demonstrating both the differential quality standards applied and the relative management utility of these two approaches.

Survey of the Microbiological Quality of Adult Bovine Rennet Extracts

Sixty-nine samples of liquid bovine rennet extract from several cheese-making plants were examined for microbiological quality. Wide differences were observed in the microbiological results, as well as in the pH, which ranged from 4.0 to 6.5, reflecting the manufacturing practices and sanitary conditions. The highest level of contamination was always caused by sporulated bacteria, both aerobic and anaerobic. Coliforms, considered to be enteric indicator bacteria were not detected, although halotolerant bacteria were found.

Virus and Bacteria Removal from Wastewater by Rapid Infiltration Through Soil

A rapid infiltration land wastewater application site, composed of unconsolidated silty sand and gravel, which has been in continuous operation for over 30 years was examined for the accumulation and/or migration of a tracer virus (coliphage f2), indigenous enteroviruses, and enteric indicator bacteria in the soils and underlying groundwater. Tracer f2 penetrated into groundwater together with the front of percolating primary effluent and was not observed to concentrate on the upper soil layers. The tracer virus concentration in a 60-foot (about 18.3-m)-deep observation well directly beneath the wastewater application area began to increase within 48 h after application to the soil. The tracer level in this well stabilized after 72 h at a level of approximately 47% of the average applied concentration. Indigenous enteroviruses and tracer f2 were sporadically detected in the groundwater at horizontal distances of 600 feet (about 183 m) from the application zone. Laboratory soil adsorption studies confirmed the poor virus adsorption observed at the site. This was especially true on surface soils when contained in wastewater. Enteric indicator bacteria were readily concentrated on the soil surface by filtration on the soil surface mat. However, during tracer f2 virus tests, comparison studies with fecal Streptococcus revealed that bacteria capable of penetrating the surface were able to migrate into the groundwater. They were detected at the same locations as tracer and enteric viruses.